1. Field of the Invention
The present invention relates to a display device, a display unit, and to a method for producing the display device and the display unit. More specifically, the present invention relates to a display device which may be used as a display of a personal computer, a mobile phone, a mobile terminal, etc., or which may be used as an independent portable display, such as a digital (or electronic) paper or a digital book that obtains information from such appliances, to a display unit which form such a display device, and to a method for producing such display device and display unit.
2. Description of Related Art
Display devices such as that shown in FIGS. 9A and 9B are conventionally known as disclosed in U.S. Pat. Nos. 4,126,854, 4,143,103, and Japanese Unexamined Patent Application, First Publication, No. Hei 1-282589. In the display device shown in FIGS. 9A and 9B, particles are used as the display medium, each of which has a hemisphere portion having a color different from the color of the other hemisphere portion. That is, a dispersed particle rotation type panel display 5 includes a capsule structure formed in a transparent substrate 2 of a plate shape in which a rotary particle 1 for display having hemispheres 1a and 1b of different colors is encapsulated and held in a space 3 of spherical shape which is filled with a dielectric liquid 4. A transparent electrode 8 including an electrode 6 and a transparent panel 7 is closely attached to the front and the back of the transparent substrate 2 and an electric field is applied by means of a power source 9 so that an image is formed by the rotation of the particles 1.
Also, a device similar to the one described above having particles of cylindrical shape is disclosed in Japanese Unexamined Patent Application, First Publication, No. 2000-89260.
In general, an electric double layer is formed around a particle which is present in a liquid due to transfer of electric charge between the particle and the liquid. As a result, the particle is electrified positively or negatively. A rotatable particle for display is formed so as to have at least two areas of different colors and different electrification characteristics in a liquid. When an electric field is applied to such a particle, one of the areas of the particle is aligned in one direction due to a torque which acts to align the pole axis of the particle with the direction of the electric field. If the direction of the electric field is reversed, the particle is turned around and the color of the particle visible from a viewpoint is changed.
Since the above-mentioned display device is of a light reflecting type device, an image formed by the display device is kind to the eye in the same way as printed matter, and does not cause eyestrain due to flickering of emitted light.
The display device may be formed by using the following method. First, the above-mentioned rotatable particles for display are mixed with an elastomer, and the mixture is thermally cured after being formed into a sheet shape. The mixture is then immersed in a dielectric liquid, such as an organic solvent or an oil. The liquid acts as a plasticizer and causes a swelling of the elastomer. Since the elastomer swells nearly uniformly, a space is generated around each particle, and at the same time, the space is filled with the liquid. As a result, the particle is held in the space surrounded by the liquid. Accordingly, the particle may freely rotate in the space. As shown in FIGS. 9A and 9B, an elastomer sheet in which particles, each of which have hemispheres of two different colors, are encapsulated in the space 3 of spherical shape filled with the dielectric liquid 4, may be obtained. The transparent electrodes are disposed so as to sandwich the elastomer sheet. The transparent electrodes may be formed by using a transparent conductive membrane made of, for instance, an indium-tin oxide (ITO).
However, there are many problems associated with the above-mentioned manufacturing method and the display device produced by using the method. That is, in the above-mentioned manufacturing method, the process is complicated due to the necessity of, for instance, the thermal curing step after the formation of the elastomer sheet or the immersion step using the dielectric liquid. Also, since the space 3 is formed by the swelling of the elastomer, the type of the liquid which can be used in the process is limited. Moreover, since the degree of the swelling of the elastomer depends on the temperature, it is difficult to obtain spaces 3 of uniform size and excellent shape, i.e., spaces 3 of spherical shape having a constant diameter. If the sizes of the spaces 3 are not uniform and the shapes thereof are irregular, a desired image cannot be produced with good reproducibility. That is, if the space 3 is too small for the rotatable particle 1, or the shape of the space 3 is distorted, the rotation of the particle in the space 3 is inhibited, and the degree of rotation of the rotary particle 1 necessary for displaying an image (180° in general) cannot be obtained when the rotary particle 1 rotates in accordance with an electric anisotropy under the influence of the applied external electric field. On the other hand, if the size of the space 3 is too large for the rotary particle 1, the ratio of the liquid portion, which does not take part in image display, to the particle portion becomes relatively too large, and it is difficult to obtain an image having an excellent contrast.